In recent years, multimedia telephone terminals which can be connected to fixed networks have been developed. These terminals provide real-time video, audio, or data, or any combination thereof, between two multimedia telephone terminals over a voice band network connection. Communication may be either one-way or two-way. Furthermore, the multimedia telephone terminals can be integrated into PCs or work stations, or can be stand-alone units.
Interworking between PLMNs (Public Land Mobile Networks) and PSTNs (Public Switched Telephone Networks) is currently being specified in third generation mobile systems. One of the items to be specified is a call type where a video/multimedia call is started with a speech phase, and during the speech phase the call is modified into a multimedia call according to the ITU-T H.324 recommendation.
Furthermore, fallback procedures have been proposed to be used in circuit-switched multimedia call setups in order to save the call in case the called party or an intermediate network does not support the requested service. To achieve this, a fallback connection, i.e. another type of connection such as a modem connection, is determined, wherein the fallback connection is established without disconnecting the calling party or performing a time-consuming error processing or messaging at the end terminals. As an example, the user may always request a fully digital UDI/RDI (Unrestricted/Restricted Digital Information) multimedia connection. Thus, the user does not have to know the capabilities of the called terminal. If it is determined, e.g. based on the ISUP (ISDN User Part) backward indicators, that the called terminal does not support UDI/RDI calls, a fallback procedure to a 3.1 kHz modem-based multimedia connection is initiated, i.e. an IWF (InterWorking Function) modem is connected to the line and the mobile traffic is modified to correspond to the (lower) data rate used by the modem connection. If there is no modem at the called party, the call is turned to a speech call, i.e. the IWF modem resource is released and the mobile traffic channel is modified to the speech modem.
However, such a fallback procedure from the UDI/RDI multimedia connection leads to the problem that the checking of the possible modem support at the called party takes several seconds. Thus, fallbacks from UDI/RDI to speech will always suffer from the monitoring delay of the modem resource. Thus, the quality of service faced by the users is reduced by the present fallback solutions.